【作者】 陈云嫩；

【导师】 柴立元；

【作者基本信息】 中南大学 ， 冶金环境工程， 2009， 博士

【摘要】 重金属废水排放不仅造成资源浪费,而且已成为饮用水源最大的安全隐患之一,其治理一直是世界环保领域的重大课题。目前,重金属废水的处理一般采用传统的石灰中和沉淀等化学法及离子交换、活性炭吸附等物理化学法,存在难以实现深度净化或成本过高等不足;另外,目前我国废麦糟年产量已达1000多万t,大多堆存处置,造成严重污染。因此,开展重金属废水深度净化及废麦糟综合利用等相关研究对保护环境具有重要意义。基于生物吸附法快速、经济、不可逆、环境友好等特性以及废麦糟量大易得的特点,同时为了顺应我国于2007年7月1日起在全国范围实施的新的《生活饮用水卫生标准》（GB5749-2005）,即将饮用水砷标准从0.05 mg/L降低到0.01 mg/L,镉的标准为0.005 mg/L。本课题选择废麦糟作为生物吸附剂的原料,以工业废水中具有代表性的阴离子砷（Ⅲ,Ⅴ）及阳离子镉（Ⅱ）为处理对象,提出了“废麦糟生物吸附剂深度净化水体中砷、镉”新思路,系统研究了生物吸附剂处理工艺参数及净化机理;突破了传统工艺处理过程需将As（Ⅲ）氧化成As（Ⅴ）再进行处理的技术瓶颈,实现了高效净化脱除水中砷、镉离子的目标。研究了废麦糟生物吸附剂处理As（Ⅲ）、As（Ⅴ）及Cd（Ⅱ）的吸附行为。筛选了深度净化砷、镉离子的废麦糟改性剂Ca（OH）₂,Ca（OH）₂的改性大大地提高了砷、镉离子的净化效率,比NaOH改性的废麦糟对As（Ⅲ）、As（Ⅴ）及Cd（Ⅱ）的吸附去除率分别提高了83.4%、37.4%和14.6%。粒度小于0.833 mm的废麦糟经改性后制备的生物吸附剂仅需1g/L的用量即可使砷、镉离子的净化效率达到最大,且其颗粒粒径对其净化砷、镉离子的影响不大;在283 K—313 K范围内,反应温度的升高有利于废麦糟对As（Ⅲ）和As（Ⅴ）的吸附,却不利于对Cd（Ⅱ）的吸附。吸附等温方程模拟分析表明,Langmuir等温式能很好地拟合生物吸附剂对砷、镉离子的吸附,在303 K时废麦糟生物吸附剂对As（Ⅲ）、As（Ⅴ）及Cd（Ⅱ）吸附的最大吸附量分别为2.125 mg/g、3.089 mg/g、2.166 mg/g。采用ζ-电位、红外光谱、能谱以及X射线衍射等手段研究揭示了废麦糟生物吸附剂对砷、镉离子的吸附机理。废麦糟表面主要为纤维素和木质素的特征官能团,生物吸附剂对砷、镉离子的吸附主要发生在细胞壁上,而且主要表现为静电吸附,其吸附作用的最佳pH值范围分别为11.5～13.0、11.5～13.0、8.0～11.5。生物吸附剂对砷、镉离子高效净化不仅因为改性剂与As（Ⅲ）、As（Ⅴ）作用分别生成Ca₅（AsO₄）₃（OH）及Ca₅（AsO₃）₃（OH）·4H₂O,与Cd（Ⅱ）作用生成Cd（OH）₂,而且生物吸附剂表面的羧基、羟基基团与砷、镉离子发生作用,羧酸中羟基被亚砷酸根（砷酸根）取代生成羧酸衍生物;羧酸中H还被亲核取代生成羧酸镉。建立了废麦糟生物吸附剂固定床吸附柱动力学数学模型,且计算了不同操作条件下的穿透曲线。利用多种反应动力学方程探究了废麦糟生物吸附剂对砷、镉离子的吸附反应动力学过程。研究表明,废麦糟吸附As（Ⅲ）、As（Ⅴ）和Cd（Ⅱ）的吸附反应是一个先快后慢的过程,符合准二级反应动力学方程,而且吸附的q_t对t^0.5曲线在50～90 min内为不通过原点的直线,说明颗粒内扩散不是控制废麦糟生物吸附剂对砷、镉离子净化过程的唯一步骤,而是由膜扩散和颗粒内扩散联合控制。与外扩散速率相比,颗粒内扩散速率大小是决定整个吸附反应速度的关键。动态工艺研究表明,穿透曲线的形状与溶液的进口流速、吸附质初始浓度以及吸附床层高度等条件有关。动力学数学模型计算结果与实验结果具有较好的吻合,验证了该模型在一定程度上的可靠性和正确性。针对实际工业废水存在其它共存离子的特点,考察了体系中多种阴离子及阳离子对废麦糟生物吸附剂深度净化砷、镉离子的影响,同时对砷、镉共存的行为进行了剖析。筛选了解吸剂,并探求了解吸温度对吸附于废麦糟中砷、镉离子的解吸效果及生物吸附剂的再生利用行为;并进行了废麦糟生物吸附剂用于深度净化湖南某冶炼厂外排废水的连续化实验研究。结果表明,进水流速为1.36 mL/min的条件下,改性麦糟生物吸附剂连续净化含砷、镉离子浓度分别为2.860和9.957mg/L的废水时,砷、镉离子的穿透时间分别为400 min和320min,经过两次吸附-再生后的生物吸附柱连续处理该废水时砷、镉离子的穿透时间分别为160 min和150 min,表明废麦糟生物吸附剂对冶炼废水具有良好的净化效果。更多还原

【Abstract】 Not only the outlet of wastewater containing heavy metals wastes lots of resourses,but also influences the safety of drinking water.So the treatment of the wastewater has always been an important project in the world environmental protection.At present,various conventional treatment methods such as lime-neutralization-precipitation,ion exchange and active carbon adsorption have a lot of shortages such as difficult to realize deeply purified or high cost.In addition,the yearly output of spent grains（SGs） is more than ten million tons in China.Most of it was deposited for disposition to lead to severity pollution.So it is of important to develop the study related to deeply purifying water containing heavy metals and the comprehensive utilization of SGs in order to protect our environment.Based on the characteristics of biosorption being a rapid,reversible, economical and ecofriendly technology and that of SGs large quantity and easy gained,deeply purified water containing arsenic and cadmium using spent grains as biosorbent technique has been put forward.Also the technique is to conform the new <Standards for Drinking Water Quality >（GB5749-2005）,brought into effect in our country at 1/7/2007,in which the concentration of arsenic has fallen from 0.05 to 0.01 mg/L,and that of cadmium is 0.005 mg/L.In the dissertation SGs was chosen as raw material for adsorbent,arsenic（Ⅲ,Ⅴ） being a representational anion and cadmium a representational cation in industrial wastewater as treating object.The treatment technics parameters and purified mechanism of SGs biosorbent for arsenic and cadmium were systemic investigated.The technical bottleneck that only under the condition of oxidating As（Ⅲ） to As（Ⅴ） can the purified water treated by traditional technology has been broken through.The objective that water containing arsenic and cadmium being high efficient purified has been achieved.The biosorption behavior of As（Ⅲ）、As（Ⅴ） and Cd（Ⅱ） from water by SGs has been analyzed.The modifier Ca（OH）₂ for SGs to deeply purified arsenic and cadmium has been chosen,which can increase the purified efficiency for arsenic and cadmium ions by a long way.The adsorptional efficiency for As（Ⅲ）、As（Ⅴ） and Cd（Ⅱ） from water by SGs can be enhanced 83.4,37.4,14.6%respectively by adding Ca（OH）₂ to SGs than that of NaOH.Only the dosage of SGs which granularity less than 0.833 mm 1 g/L after modified to be biosorbent can get to the maximum efficiency for arsenic and cadmium.The particle size of biosorption has little effect on the purifying process.The sorption of As（Ⅲ） and As（Ⅴ） increased with increase in contacting temperature at 283 K—313 K,but sorption of Cd（Ⅱ） go against with it.The simulated analysis indicated that Langmuir isotherm was well fit to the experimental data of sorption of As（Ⅲ）、As（Ⅴ） and Cd（Ⅱ） by SGs.At 303 K the maximum sorptional capacity of As（Ⅲ）、As（Ⅴ） and Cd（Ⅱ） were 2.125、3.089、2.166 mg/g,respectively.Through various testing means such asξ-potential,Fourier transform infrared absorption spectrum,energy spectrum and X-ray diffraction,the biosorptional mechanism of biosorption of arsenic and cadmium ions by SGs biosorbent to has been put forward.The characteristic of cellulose and lignin were the mainly function groups at the surface of SGs.The biosorption of arsenic and cadmium ions occurred mainly at the cell wall of biosorbent.And static sorption between SGs and As（Ⅲ）、As（Ⅴ） and Cd（Ⅱ） were mainly biosorptional mechanism,which the optimal pH were 11.5～13.0、11.5～13.0、8.0～11.5,respectively.The high efficient for purifying arsenic and cadmium ions by biosorbent,not only for the modifier interacting with As（Ⅲ）、As（Ⅴ） to make Ca₅（AsO₄）₃（OH） and Ca₅（AsO₃）₃（OH）·4H₂O,respectively,and with Cd（Ⅱ） to gain Cd（OH）₂,but the carboxyl and hydroxyl groups at the surface of SGs were interacted with arsenic and cadmium ions.The hydroxyl in carboxylic acid was replaced by arsenite or arsenate to yield carboxylic acid ramification,and hydrogen H in carboxylic acid to obtain carboxylic acid cadmium.The kinetics mathematical model of sorption column packing SGs biosorbent was established,and the breakthrough curve under different conditions was calculated.Using various kinetics equations the sorption kinetics process of arsenic and cadmium by SGs biosorbent was discussed.The study indicated that the sorption for As（Ⅲ）、As（Ⅴ） and Cd（Ⅱ） by SGs was a rapid first and slow later process,which according with pseudo second-order kinetics equation.The curve q_t to t^0.5 of sorption being a line not through initial point at 50～90 min illuminated the interior diffusion was not the only rate-limiting step at purifying process for arsenic and cadmium by SGs,but united-controled by film diffusion and granule interior diffusion.Compare with the rate of extenal diffusion,that of granule interior diffusion was a key deciding the whole sorption process.At dynamic process,the figure of breakthrough curve was related to experimental conditions,such as flow rate of solution, initial concentration of sorbate and the column height.The calculated result through kinetics mathematical model was coincidence with the experimental result,which to some degree validated the reliability and correctness of model.Aimed at the fact that other ions being in the actual industrial wastewater,the effect of various anions and cations in the system on sorption of arsenic and cadmium by SGs was studied.At the same time, the behavior of arsenic and cadmium coexist was also analyzed.The strippant was chosen,and desorption temperature that affect the desorption process on arsenic and cadmium from SGs were investigated. Meanwhile,the regeneration utilization behavior of biosorbent was researched.Moreover the continuum-experimental study on deeply purified the outlet wastewater from one metallurgical plant at Hunan by SGs biosorbent was fulfilled.The results indicated that at inlet velocity of flow 1.36 mL/min,the time of break-through were 400 min and 320 min for arsenic and cadmium,respectively when using SGs to continuously purify the wastewater containing 2.860 mg/L of arsenic and 9.957mg/L of cadmium.After two rounds of sorption-regeneration the times of break-through were 160 min and 150 min for arsenic and cadmium, respectively adsorpted by biosorbent,which indicated that the SGs biosorbent has highly purified effect for metallurgical wastewater.更多还原